Hey guys,
I'm stripping the undercoating in order to find and address hidden rust areas, and intend to paint it afterwords. This seems to be effective in new cars (my 2001 Silverado still seems clean underneath, a testament to the improvements in paint in the last 30 years) and this car will never see a winter road again, so I'm thinking paint should be sufficient.

I have found a few areas with pinholes in the floorboards which I intend to reinforce with fiberglass (from the inside) after a thorough wire brushing down to bare metal. The front passenger side will be completely replaced with a toe panel from a donor car and a new patch floor panel. After this, the remaining rust areas will be treated with POR. Finally, I'm planning on coating the inside with spray-in bed liner material.

As for the underside, after all this is done, what's the most durable (black) paint? Suggestions I've received so far were:

Implement (tractor) paint

Catalyzed acrylic urethane enamel

basic lacquer

rustoleum

spray-in bedliner material (ugly but tough)

What results have you guys had? Do you have a favorite? What other suggestions do you have?

I am working toward this on my 81, so I 'm looking forward to some of the responses. I am leaning toward an epoxy primer, Maybe ppg's DP90.

Also I am a big fan of Eastwoods chassis black. They now offer it in different levels of gloss. They also now have a chassis black primer. I bought these new products for some of my suspension parts. Maybe I can have some pics by the end of the week. I used the original Eastwood chassis black on my 72 and its nice.

I also have some pinholes in my floor. I was going to try to mig them up instead of the fiberglass. Not sure if it will burn through or not.

It seems to have been very effective as a preservative, but there were a few places on my car where (after 30 years) it had started to lose its grip on the steel, or else the GM sealer had lost its grip and the undercoating fell away with the sealer. Either way, it had formed a pocket for moisture to collect and stay in.

Asphault undercoating takes a special heated sprayer for application (this is NOT the same thing as "rubberized undercoating" available at the auto parts store) but places like Ziebart and dealerships usually have this equipment.